There were reports of the igb driver unmapping buffers without calling
dma_mapping_error. On closer inspection issues were found in the DMA debug
API and how it handled multiple mappings of the same buffer.

The issue I found is the fact that the debug_dma_mapping_error would only set
the map_err_type to MAP_ERR_CHECKED in the case that the was only one match
for device and device address. However in the case of non-IOMMU, multiple
addresses existed and as a result it was not setting this field once a
second mapping was instantiated. I have resolved this by changing the search
so that it instead will now set MAP_ERR_CHECKED on the first buffer that
matches the device and DMA address that is currently in the state
MAP_ERR_NOT_CHECKED.

A secondary side effect of this patch is that in the case of multiple buffers
using the same address only the last mapping will have a valid map_err_type.
The previous mappings will all end up with map_err_type set to
MAP_ERR_CHECKED because of the dma_mapping_error call in debug_dma_map_page.
However this behavior may be preferable as it means you will likely only see
one real error per multi-mapped buffer, versus the current behavior of
multiple false errors mer multi-mapped buffer.